Thermodynamic method for analyzing and optimizing pretreatment/anaerobic digestion systems

This paper builds a quantitative thermodynamic model for the microbial hydrolysis process (MHP, which uses Caldicellulosiruptor bescii at 75°C pre-digestion) producing biogas from 5-10% aqueous suspension of dairy manure (naturally buffered near pH 7.8 by ammonium bicarbonate) anaerobic digestion with mix acetoclastic and syntrophic methanogenesis. Standard Gibbs energy changes were calculated major reactions in pre-digestion, H2, acetate, CO2 digester, methanogenesis digester. The available data limit study to analyzing digester short-chain volatile fatty acids anions. Results are presented as curves ΔrxnG (Gibbs change) vs. acetate concentration. H2(aq) concentration must be above 1.2×10-9 M get significant methanogenesis, i.e., negative. results show propionate, butyrate, valerate slows increases because hydrogen production also decreases, consequently, increases. Bicarbonate inhibits both but is necessary prevent acidification (souring) At identical steady-state conditions, runs about 1.4 times faster than Because produces catabolized methanogens, types methanogens maximize production. culture predicted evolve optimize ratio condition signaled constant, low effluent. Obtaining solids reduction high 75% MHP requires feedstock less 25% lignin their symbiotic bacteria.